Operation of off-road and agricultural vehicles is simplified by locating operator controls which require viewing near the line of sight of the operator. As a result, heating and cooling controls, and the energy transfer mechanisms associated therewith (heating and cooling heat exchangers) in vehicles such as combines have conventionally been located at the center and top of the operator cab near the line of sight of the operator. In particular, the control knobs, the blower, and the heat exchangers are typically at the top and center of the cab. In this configuration, the blower and heat exchangers are positioned at the same location as the control knobs to simplify the mechanical link between the control knobs and the heat exchanger valves. Another reason the blower and heat exchangers are located at the top center of the cab is to provide a relatively efficient use of cab space.
Despite the advantages of locating the heating controls and associated heat transfer devices at the top and center of a cab, there are some disadvantages. One such disadvantage is that the cost of providing water and refrigerant lines to the coils is relatively high. More specifically, the hot water source (e.g., engine) and refrigerant source (e.g., compressor on the engine) in a combine are relatively distant from the top and center of the cab. However, if the heat exchangers and associated valves are displaced from the control knobs, the routing of the mechanical link therebetween becomes difficult and expensive. Another disadvantage caused by locating the heating coil at the top and center of the cab is the inability to effectively heat the lower portions of the cab, such as at the operator's feet.
U.S. Pat. No. 5,538,472 for "Agricultural Vehicle Cab Temperature Control System" discloses an agricultural vehicle such as a combine in which the heat exchangers are relocated from the typical location adjacent the heating controls at the top and center of the operator cab to a location such as below the operator seat, with the heating controls electromagnetically linked to the heat exchangers. This spacial arrangement allows the conduits for heat transfer fluid to be simplified because the heat exchangers are located closer to the heat source than in the prior art systems.
Operator comfort within the cab of an agricultural vehicle such as the one described in the above-identified patent may be affected by a number of external factors. For example, changes in ambient air temperature can lead to undesired changes in the cab air temperature, which decreases operator comfort. In addition, operator comfort in the cabs of such vehicles can be adversely influenced by solar loading on sunny days. This results from the functional cab design of such vehicles which requires large front and side windows to maximize visibility to crop as it enters the machine and good visibility to the sides. These front and side windows may extend from the floor to headliner, but behind the cab there may be only a small window to allow visibility into a grain tank which typically blocks sunlight from the rear. Thus, operator comfort in such cabs is significantly influenced by the position of the sun and the direction of travel. More particularly, the operator can feel the radiant heat from sunlight when traveling towards the sun or at right angles to the sun but does not feel it when traveling away from the sun.
In systems requiring manual setting of the heat energy output of the heat exchangers, operators may find it difficult or even impossible to continually monitor and change the settings as needed to compensate for such external influences and maintain a desired cab air temperature. Accordingly, it would be desirable to automatically control the amount of heating or cooling and the fan speed to maintain a constant, desired temperature in the cab without need for operator intervention.